Austenitic chromium-nickel and/or manganese steels



Patented Nov. 23, 1943 AUSTENITIO CHBOMI'UM-NICKEL AND/OR MANGANESE STEELS Russell Franks, Niagara Falls, N. Y., assignor to Elcctro Metallurgical Company, a corporation of West Virginia No Drawing. Application February 4, 1942, Serial No. 429,500

Claims.

This invention relates to austenitic chromiumnickel steels and to articles made therefrom,'and has as its primary object the improvement of the physical characteristics and corrosion resistance of such steels.

Chromium steels find numerous and varied uses primarily because of their exceptional res stance to attack by corrosive media and the ready ability of the steels to be fabricated into different kindsof equipment. In general, the steels exhibit excellent resistance to oxidizing corrosive media, although the ability of the steels to resist attack by reducing corrosives is not as great as with corrosives of an oxidizing nature.

Nickel in amounts hereinafter discussed, aside from improving certain physical characteristics of chromium steels, also effects some improvement in their resistance to reducing corrosives, such as those containing sulfuric, acetic or hydrochlorlc acid. However, even with nickel prescut, for example as in stainless steel of the 18% chrbmium-8% nickel type, the resistance of the steel to reducing type corrosives is limited and their usefulness depends primarily upon their resistance to corrosion of an oxidizing nature.

Manganese in appropriate amounts may be advantageously added to chromium steels to give the high degree of workability and other properties imparted by nickel. Manganese improves the resistance of chromium steels to attack from certain corrosive media, for example, sulphurous acid and sulphur-containing gases. Corrosionresistant austenitic chromium steels in which manganese replaces nickel, or which contain both manganese and nickel, still are limited in their resistance to reducing corrosives and find their major field of usefulness in resistance to oxidizing types of corrosive media.

A further improvement in the ability of the steels to resist reducing corrosives may be obtained by additions of molybdenum. While broadening the utility of chromium-nickel steels for certain purposes, molybdenum additions tend to affect detrimentally the hot working characteristics of the steel. Whe'n'several per cent of molybdenum are present, for example in 18% chromium-8% nickel steel, it is necessary to increase the nickel content to between 12% and 14% in order to maintain satisfactory hot working properties. Even with this increase in the nickel content, the steel is more difficult to hot work than 18% chromium-8% nickel steel without molybdenum.

' Broadly the present invention comprises cast and wrought austenitic steel containing between 12% and 30% chromium and at least'5% but less than 20% of an austenite-forming element from the group consisting of nickel and manganese wherein the resistance of .the steel to reducing corrosives and its ability to be machined' are considerably enhanced by alloying therewith small but effective amounts of antimony.

More specifically the invention contemplates alloy steels containing in addition to antimony, chromium between 12% and 30%, at least 5% but less than 20% nickel or manganese or both,.

up to 1% silicon, up to 0.30% of carbon or nitrogen or both, remainder being principally iron. In wrought steels the antimony should not greatly exceed about 0.50%, and in cast steels about 1.50%. It is preferred that these percentages of antimony be added to steels containing chromium between 15% and 25%, nickel between 5% and 15%, manganese up to 5%, not over 0.15% carbon or nitrogen or both, and otherwise as shown in the broader range.

Antimony additions improve both the corrosion resistance and machinability of chromiumnickel steels containing in addition to the constituents previously mentioned between 0.5% and 3.5% molybdenum. It is preferable that the molybdenum content be between 0.50% and 2%, chromium between 16% and 24%, nickel between 8% and 18% and carbon or nitrogen or both up to 0.15%. Higher molybdenum content steels, when heated under certain necessary conditions during fabrication and use, are subject to the development of a brittle constituent generally referred to as sigma phase. This difflculty may be overcome by lowering the molybdenum content to about 2% and adding antimony in accordance with the invention. Steels of this composition are relatively free from the sigma phase constituent and have excellent re- 16% and 24%, nickel between 6% and 16% and carbon or nitrogen or both up to 0.15%.

It has been found that a high recovery of antimony is obtained, in fact 95% of the antimony introduced into the molten steel is retained in the finished product. Antimony, when used within the limits hereinbefore described, enters into solid solution with the steel and hence results in a product of exceptionally uniform characteristics.

Antimony, likewise, is retained in weld deposits made with antimony-bearing chromium-nickel steel welding rods, thus the inherent corrosion resistance imparted by the antimony addition is retained in the resulting weld. This is particularly important when the base metal and welding rod are of similar composition. If the antimony were not recovered in the weld deposit, the resulting weld would be inferior in corrosion resistance to the base metal in which the weld is made. Antimony-bearing welding rods prepared from steels of the compositions hereinbefore described are particularly suitable for welding chromium-nickel steels with or without additions of ferrite-promoting elements such as molybdenum and columbium. The general practice in welding such steels has been to employ welding rods having somewhat higher alloy contents, for example chromium and nickel, in order to compensate for loses during welding and to assure comparable corrosion resistance in both the weld and the base metal. Welding rods having compositions within the limits of the present invention can be successfully employed in welding chromium-nickel steels with or without columbium or molybdenum due to the inhibiting efiect of the antimony addition on corrosive attack by reducing corrosive media.

In order to illustrate typical advantages of antimony additions to austenitic chromium-nickel steels, Tables I to IV set forth experimental data on certain effects of antimony additions on austenitic stainless steel of the 18% chromium-8% nickel type with and without molybdenum.

Table I sets forth the analysis of the steels. Of these, the first group (Heats 1 to 6) were subjected to hot forging and rolling treatments at between 1200 C. and 900 C. The first four heats, reaching a maximum antimony content of approximately 0.50%, showed good. hot working properties and were forged and rolled without cracking between the temperatures indicated. Heats and 6, however, having an antimony content considerably in excess of 0.50% cracked badly during the forging treatment. The second group of heats (7 to 11) with antimony additions exceeding 0.50% were not subjected to hot working and their properties will be considered only in the cast condition. The third group of heats (12 to 18) containing molybdenum with and without antimony not exceeding 0.35%v all exhibited excellent hot working characteristics.

The straight 18-8 type wrought steels (Heats 1 to 6) were subjected to machining tests. These tests were made with standard high speed steel tools using a depth of'cut of 0.1" and a feed of 0.018". Heat No.1, containing no antimony, machined satisfactorily at speeds up to 75 feet per minute; Heat No. 2, with 0.15% antimony, up to 90 feet per minute; Heat No. 4, with 0.54% antimony, up to 114 feet per minute. With above approximately 0.50% antimony, no further improvement in machinability was evidenced.

Table II comprises data relating to the mechanical properties of these steels. In the table the abbreviated headings represent respectively the yield point in pounds per square inch, tensile strength in pounds per square inch, per cent elongation in two inches, per cent reduction in area, Izod impact in foot pounds and Brinell hardness number. The data illustrate that there is no substantial alteration in the mechanical properties of the wrought steels containing up to about 0.50% antimony. This is true for the straight 18-8 type steel of group 1 (Heats 1 to 4) and the molybdenum-containing stainless steels of group 3 (Heats 12 to 18). With cast steels, group 2 (Heats '7 to 11) if a high degree of toughness and ductility are to be maintained it is desirable to limit the antimony addition to about 1.50%.

Table 111 comprises the results of a series of corrosion tests in 65% boiling nitric acid.

Table IV comprises the results of similar tests in hydrochloric and sulphuric acid at room temperature.

These tests were conducted using three separate 48 hour periods to establish whether the corrosion rate of the steels was uniform, accelerated or decreased as the interval of test was increased. If the corrosion rate remains constant or decreases with increase of time, the utility of the material for a given purpose can be determined. However, if the corrosion rate increases with increase in time even an approximation of the amount of metal that will be corroded away under given conditions is unreliable and the utility of the materialis therefore considerably curtailed.

TABLE I Analysis of steels Heat Condition of Cr Ni Mn 81 0 Mo Sb steel l Per- Pcr- Per- Per- Per- Per- Percent cent cent cent cent cent 1 19. 04 9. 24 1. 5i 0. 35 0. 05 None Hot worked. 2. 8. 1. 53 0.45 0.07 0.15 Do. 3. 8. 91 1. 49 0. 35 0. 08 0. 31 D0. 4. 8. 74 1. 47 0. 34 0. 07 -0. 54 Do. 5 8. 93 1. 53 0.40 0. 06 0.73 6 8. 93 1. 53 0. 37 0.05 l. 03

9. 13 1.56 0.44 0.05 None Cast. 9. 01 1. 62 0. 48 0. 07 0. 51 Do. 9.11 1. 56 0.42 0.08 l. 01 Do. 9.04 l. 58 0.42 0.08 1. 54 Do. 9. 04 1. 55 0. 43 0. 07 2. 00 Do. 12.01 1.44 0.36 0.06 None None Hot worked. 11. 58 l. 55 0.45 0. 06 1.03 None Do. 12. 03 1. 57 0. 43 0.05 1. 02 0. 33 Do. 12.34 1.54 0.44 0.05 2. 18 None Do. 11. 99 1. 63 0. 48 0. 07 l. 92 0. 32 Do. 12.34 1. 57 0.46 0.04 3. 57 None Do. 11. 94 l. 54 0. 47 0. 07 3. 52 0.35 Do.

1 All samples air cooled from 1100 C. Partially hot worked-steels cracked upon forging.

The data of Table III show conclusively that the presence of antimony in wrought or cast austenitic chromium-nickel steels, with or without molybdenum, has little or no effect upon the resistance of the steels to oxidizing corrosive media.

The superiority of antimony-containing stainless steels in resisting reducing type corrosive media over antimony-free stainless steels is shown in Table IV. The data indicate that the resistance of wrought steels containing antimony Another important factor,

However, as afore- With antimony (No. corrosive action This is Condition 01' steel 1 Do. Do. Do.

There is a very definite decrease 2,384,070 TABLIII 36 48-111. period 0. 0169 Wrought. 0. 0049 0. 0031 0. 0009 definitely increases with time. The cast period tended, whereas with the antimony-free sample the rate stainless steel samples containing antimony (Heats 8 to 11) likewise exhibit a marked improvement in resistance over sample 7 containing no antimony. in the corrosion rate of the steels with increase in antimony content up to 2%. .mentioned, if a high degree of ductility and toughness are required in these steels the antimon-y should not greatly exceed 1.5%. wrought molybdenum-containing steels (Heats Nos. 14, 16 and 18) the phenomenon is no less pronounced. For example a steel containing 1% molybdenum, with 0.33% 14) is equally as resistant to the r. 40 of 10% hydrochloric acid at room temperature as the 2% and 3.5% molybdenum steels without antimony (Nos. 15 and 17 respectively). a definite indication that the cheaper metal antimony may be substituted for a portion of the more expensive metal molybdenum with no sacriflce in the corrosion resistance of the steel to this type of corrosive. Further economy maybe 10% sulphuric acid room temp.

period Condition of steel 1 Do. Do

Do. Do. Do. Do.

3d 48-hr. 1st 48-hr. 2d 48-hr.

period 0007 Cast.

0005 Wroueht.

TABLE IV Inch penetration per month Mechanical pmp ttea of antimony-Denim rs-s chromium-nickel steels period 2d is-hr.

0.0005 0.0005 Wrought. 0.0006 0.0005

chromium-nickel steel 10% hydrochloric acid room temp.

period 1st 48-111. 2d 48-hr.

period period period TABLEJII None 0 None 0 0.33 0 None Hydrochloric and sulphuric acid tests on 18-8 None n... t .L .ml .0... h mw mmmn mmmp mmmmmmm m w m w mmm mmmm mmmmm mtmmmmm h m mwwm ammo" mmwmwnm m J 1m H m. manna nmnmm nnmmwom mm m n P m Momma nwmmm ma num IUD w E m H "m m m mmm m r Rummy manna mammmwa M ma m fi m mm m r amnm aamwm anmnana 80ml B 39295 a moat mam... m z m z M m m m m m m m Nrliss P m m m m m m a m I n I n a m m m m m m m l naen LSLMH n 18-8 chromium-nickel steels Percent Percent Percent 1,

Heat N0.

1 All samples air cooled from 1100 0.

Heat No.

Boiling nitric acid tests on antimony-bearing 1 All samples air cooled from 1100 C.

1 All samples air cooled from 1100" C.

obtained in that less nickel is required to preserve good hot working properties in the lower molybdenum-content steels.

It is to be understood that the invention is in no way limited by the particular compositions set forth in the tables. The compositions and data recorded therein are merely illustrative of the effect of antimony in a preferred embodiment of the present invention.

In my copending application, Serial No. 429,499, filed February 4, 1942, there is disclosed the effect of small additions of antimony upon the properties of 4% to 30% chromium steels.

What is claimed is:

1. Austenitic alloy steel containing between 12% and 30% chromium; at least and up to 16% of an austenite-forming element from the group consisting of nickel and manganese; between about 0.1% and 1.5% antimony; remainder principally iron together with incidental impuri.. ties; the antimony serving to increase the resist ance of the alloy in both the wrought and cast condition to attack from reducing-type corrosives without impairing the resistance of said alloy to oxidize corrosive media.

2. Austenitic alloy steel containing between 15% and 25% chromium, between 5% and 15% nickel; between about 0.1% and 1.5% antimony; remainder iron and incidental impurities including not over 5% manganese, 1% silicon, 0.15% in the aggregate of carbon and nitrogen; the

nickel and manganese amounting in the aggre gate to not over 16% and the antimony serving to increase the resistance of the alloy in the ascast condition to attack from corrosives of a reducing nature without impairingthe resistance of said alloy to oxidizing corrosive media and without materially lowering its toughness and ductility.

3. Austenitic alloy steel containing between 15% and 25% chromium, between 5% and 15% nickel; between about 0.1% and 0.50% antimony; remainder iron and incidental impurities including not over 5% manganese, 1% silicon, 0.15% in the aggregate of carbon and nitrogen; the nickel and manganese amounting in the aggregate to not over 16%; and the antimony serving to increase the resistance of the alloy in the hotworked condition to attack from reducing type corrosives and to improve its machinability without impairing its resistance to corrosives of an oxidizing nature or impairing its physical properties.

4. Austenitic alloy steel containing between 12% and 30% chromium; at least 5% and up to 16% nickel; between 0.1% and 6.5% in the aggregate of at least one ferrite-promoting element from the group columbium and molybdenum, the columbium not to exceed 3%, the molybdenum not to exceed 3.5%; between about 0.1% and 1.5% antimony, remainder iron and incidental impurities including not over 0.30% carbon; the antimony serving to improve the corrosion resistance of the steel to reducing corrosive media without impairing its resistance to oxidizing corrosive media.

5. Austenitic alloy steel containing between 16% and 24% chromium, between 8% and 16% nickel, between 0.5% and 2.0% molybdenum; between 0.1% and 1.5% antimony; remainder iron and incidental impurities including not over 0.30% carbon; the antimony serving to improve the corrosion resistance of the steel to reducing corrosive media without impairing the resistance of said alloy to oxidizing corrosive media and without the formation of detrimental amounts of embrittling sigma phase constituents, such as are formed in higher molylenumcontent steels.

6. Austenitic alloy steel containing between 16% and 24% chromium; between 6% and 16% nickel; between 0.1% and 1.5% columbium; between 0.1% and 1.5% antimony; remainder iron and incidental impurities including not over 0.30% carbon; the antimony serving to improve the resistance of the steel to attack from reducing type corrosive media without impairing its resistance to intergranular corrosion and to corrosive media of an oxidizing type.

7. Austenitic 18% chromium-8% nickel stainless steel containing between 0.1% and 0.5% antimony characterized in that the steel exhibits enhanced qualities of machinability and corrosion resistance over similar steels without antim.

8. A welding rod characterized in that it contains between 12% and 30% chromium; at least 6% and up to 16% of an austenite-forming element from the group consisting of nickel and manganese; between about 0.1% and 1.5% antimony; remainder principally iron with incidental impurities including not over 0.30% carbon; said welding rod being particularly suitable for pro ducing welds having high resistance to attack from corrosives of a reducing nature.

9. A welding rod characterized in that it contains between 16% and 24% chromium; at least 6% and up to 16% nickel; between 0.1% and 6.5 of a ferrite promoting element from the group columbium and molybdenum, the columbium not to exceed 3.0%, the molybdenum not to exceed 3.5%; between 0.1% and 1.5% antimony; remainder iron and incidental impurities including not over 0.30% carbon; said welding rod being particularly suitable for welding members employed at elevated temperatures and requiring high resistance to attack from corrosives of a reducing nature,

10. Austenitic alloy steel containing between 12% and 30% chromium; at least 5% but less than 20% manganese; between 0.1% and 1.5% antimony; the remainder iron and incidental impurities; the antimony serving to increase the resistance of the alloy to attack from corrosives of a reducing nature without impairing its resistance to corrosives of an oxidizing nature or substantally impairing its physical properties.

RUSSELL FRANKS.

CERTIFICATE OF CORRECTION. Patent No. 2,551.},870. November 23, 1915. V

RUSSELL FRANKS.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows Page 14., first column, line 25, for oxidize" read --oxidizing--; and second column, line 11;, for "molylenum" read "molybdenum"; line 145, after "6. 5" insert and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Sigmed and sealed this 18th day of January, A. D1 19%.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents. 

